Structural and gold mineralizing evolution of the world-class orogenic Mana district,Burkina Faso: Multiple mineralizing events over 150 million years     

《Ore Geology Reviews》2017

The Mana district, located in the northern part of the Birimian Houndé greenstone belt in western Burkina Faso, is a world-class Paleoproterozoic orogenic gold district (∼8 Moz) including five gold deposits (Fofina, Nyafé, Siou, Wona-Kona and Yaho). These deposits are located in specific lithostratigraphic domains, and gold is controlled by various structural features. Deposit- and regional-scale mapping, intrusion age and geochemistry, as well as airborne aeromagnetic and electrical resistivity geophysical data, were used to decipher the tectonic evolution of each gold deposit and the district. Five deformational and four gold mineralizing events were recognized.The first deformation event (D1_MD: E-W oriented shortening) affected the metamorphosed volcanic and sedimentary rocks of the Lower Birimian group. This early deformation episode was correlated with the formation of gently N-plunging folds (F_1MD) and N-S-striking thrusts faults coeval with emplacement of the pre- to synkinematic Wona-Kona and Siou plutons dated at ∼2172 Ma, under greenschist facies metamorphism. The quartz-carbonate veins (V_1MD) at Fofina and Siou formed during D1_MD at Eoeburnean time, manifesting the first gold event at approximately ∼2172 Ma.The following deformation event (D2_MD: E-W oriented extension) is associated with the deposition of the Upper Birimian group (Mana basin) overlying the Lower Birimian group. The geometry of the Mana basin is controlled by the Mana and Maoula shear zones. The Tarkwaian-type rock formation overlying the Upper Birimian group, controlled by the Wona-Kona and Siou shear zones, is constrained at the end of D2_MD or at the beginning of the D3_MD event with a maximum deposition age at ∼2113 Ma.The third deformation event (D3_MD: E-W to WNW-ESE transpression) affected the entire supracrustal rock. Such event is correlated with the formation of map-scale F_3MD folds and dextral shear zones during the Eburnean orogeny (∼2113–2090 Ma). A second gold mineralizing event occurred during D3_MD and is manifested by quartz-carbonate veins (V_3MD) and disseminated sulfides at the Yaho, Fofina and Nyafé and possibly Wona-Kona deposits.The fourth deformation event (D4_MD: NNW-SSE transpression) is correlated with sinistral shearing along the major transcurrent faults and the development of asymmetric NNE-striking folds (F_4MD) associated with vertical fold axes. Syn-D4_MD mineralization is characterized mainly by a strong silicification (Si_4MD) with disseminated pyrite and arsenopyrite along the Wona-Kona shear zone and by tiny quartz-carbonate veinlets (V_4MD). This event is considered the main gold-bearing event in the western margin of the Mana district.The fifth and last deformation event (D5_MD) is brittle in character and was responsible for the formation of E-W subvertical crenulation cleavages and reverse faults under overall N-S shortening. This late deformation event is tentatively associated with a last gold event recorded as free gold associated with muscovite in brittle fractures developed in competent orebodies at the Wona-Kona and Siou deposits. This event could be as young as ∼2022 Ma, the age obtained from Ar-Ar datation of muscovite-schists at the Wona-Kona deposit.Our main contribution is that we decipher multiple gold mineralizing events at the district scale based on deposit- and regional-scale mapping. It is interpreted that gold was introduced as early as ∼2172 Ma and possibly as late as ∼2022 Ma during at least 3 or even 4 shortening tectonic events in a timeframe not yet recognized at the district scale for all the Birimian belts.  相似文献   

中非裂谷系前寒武系基岩油气成藏组合   总被引：1，自引：0，他引：1  

窦立荣  王景春  王仁冲  魏小东 《地学前缘》2018,25(2):15-23

中非裂谷系是在前寒武系结晶基岩基础上发育起来的中新生代裂谷盆地群。通过露头和钻井资料研究发现,基岩主要由前寒武系岩浆岩、正变质岩和少量副变质岩组成。根据暗色矿物含量可以将基岩划分为长英质和铁镁质岩石两大类,前者更有利于风化和裂缝的形成,储层物性较好。寒武纪-侏罗纪长期风化作用形成了广泛分布且厚度较大的球形风化壳(段),早白垩世中非剪切带的走滑拉张应力场与前寒武系刚性基岩的耦合作用在基底产生了大量高角度断层、共轭缝、微裂缝和节理等,风化淋滤、表生和热液作用控制了溶蚀、胶结和次生孔隙发育。风化壳和裂缝储层发育具有“似层状”的特征,垂向上基岩潜山储层序列可进一步划分为风化淋滤带、裂缝发育带、半充填裂缝带和致密带四个区带。中非裂谷系盆地在早白垩世、晚白垩世和古近纪三期裂谷期发育了三期区域性厚层泥页岩,古近系暗色泥岩由于埋藏浅,处于未成熟阶段,不能作为有效烃源岩,上白垩统泥岩以滨浅湖相为主,有机质含量总体不高,以Ⅲ型干酪根为主,下白垩统深湖相泥岩是区域上的优质烃源岩,同时为基岩提供了良好的油源和顶盖层。根据盖层的时代,可以划分出下白垩统、上白垩统和古近系3类成藏组合。乍得Bongor盆地基岩勘探获得极大成功,发现了一批高产稀油油田,打开了中非地区一个新的油气勘探领域。  相似文献   

全球化下"跨国移民社会空间"的地方响应——以广州小北黑人区为例   总被引：11，自引：5，他引：6  

李志刚  薛德升  杜枫  朱颖 《地理研究》2009,28(4):920-932

全球化下的中国城市社会空间面临新的重塑,以诸多大城市新近出现的跨国移民社会空间的发展最为突出。本文以广州小北黑人区为研究对象,采用三角检验法,综合利用问卷调查、深度访谈等研究手段,探讨全球化下中国城市所出现的新社会空间的地方响应。总体上,一个负面的黑人群体形象已经被建构起来。就居民的年龄、性别、教育水平、居住时间和宗教信仰等方面而言,各类本地居民在对黑人聚居的看法上并无太大差别;但不同职业类型的居民看法差别很大。排斥心理的产生多源于外在信息的影响,亦即本地媒体排斥、矮化性的负面响应。  相似文献   

华北大陆南缘中、新元古代大陆边缘性质及构造古地理演化   总被引：13，自引：2，他引：11  

周洪瑞  王自强 《现代地质》1999,13(3):261-267

华北大陆南部中、新元古代大陆边缘的演化经历了复杂的过程。从沉积类型、沉积组合、火山活动和花岗岩性质分析入手, 探讨了华北大陆南缘中、新元古代大陆边缘的性质和演化历程。将其演化历史分为４ 个阶段： （１） 裂陷火山活动阶段（ 长城纪） ; （２） 拗陷、充填阶段（ 蓟县纪） ; （３） 差异升降、充填封闭阶段（ 青白口纪） 和（４） 活动大陆边缘发展和大陆增生阶段（震旦纪—早古生代） 。  相似文献   

Contrasting CW and CCW tectono-metamorphic belts in the eastern Himalayan syntaxis: quantification of P–T–t paths and tectonic interpretation     

《Gondwana Research》2020

In the eastern Himalayan syntaxis, the Indus–Tsangpo Suture Zone separates the Himalaya to the south from the southern Lhasa terrane to the north. In this study, we combine petrology, zircon U–Pb geochronology and phase equilibrium modeling to quantify the P–T–t paths of metapelites from the Namche Barwa complex, part of the Himalaya, and the Nyingchi complex, part of the southern Lhasa terrane. The Namche Barwa complex is interpreted to record slow cooling across a HP granulite facies P–T field at >12 kbar from 790 °C to the solidus at 750 °C between c. 50 Ma and c. 17 Ma, followed by decompression with slight heating to a P–T field at 5.5–8 kbar and 790–825 °C at c. 3 Ma, consistent with the post-peak segment of a CW P–T–t path. By contrast, the Nyingchi complex records a CCW P–T–t path characterized by compression through peak granulite facies P–T conditions of 7.5–9 kbar at 760–780 °C, before re-crossing the solidus at P of ∼11 kbar at c. 35–31 Ma. Based on the youngest published spot date from a detrital core in zircon from metapelite, the maximum depositional age for the protoliths of the Nyingchi complex is c. 53 Ma. We propose a tectonic scenario in which the Nyingchi complex (CCW P–T–t path) was buried in the interval c. 53–35 Ma synchronous with heating then compression during ongoing convergence related to the India–Asia collision. By contrast, the Namche Barwa complex (CW P–T–t path), which represents the subducted Indian continental lithosphere, records relatively fast exhumation from c. 17 to c. 3 Ma that was initiated by crustal-scale folding linked to orogen-scale gravitational spreading and thrusting, enhanced by surface processes.  相似文献   

Geological Setting and Controls on the Development of Graphite, Sillimanite and Phosphate Mineralization within the Jiamusi Massif: An Exotic Fragment of Gondwanaland Located in North-Eastern China?     

Simon A. Wilde  Helen L. Dorsett-Bain  Robert G. Lennon 《Gondwana Research》1999,2(1):21

China is the world's biggest producer and exporter of graphite and also possesses the world's largest reserves of crystalline graphite. One of the main production areas is in northeastern China around Jixi, in Heilongjiang Province, where graphite, sillimanite and phosphate form in original sedimentary horizons within the Mashan Group. The Mashan Group is composed of khondalitic metasediments and tectonically interleaved orthogneisses, all metamorphosed to granulite facies. The peak conditions have been calculated at 800–850°C at 5.3–6.2 kb and the P–T–t path defines a tight clockwise loop involving simultaneous decrease in temperature and pressure, falling to 410–490°C at less than 3 kb. This metamorphic event is interpreted as resulting from continent–continent collision, with emplacement of mantle–derived mafic magma and possible delamination at the base of the crust. Metamorphism has been precisely dated at 500 Ma, using U–Pb zircon SHRIMP techniques. It appears likely that this terrane formed part of an originally more extensive orogenic belt of Late Pan–African age. Rocks of similar age are recorded from east Antarctica, Western Australia, India and Sri Lanka, suggesting that the Mashan Group was most likely juxtaposed with these areas within Gondwanaland. The mechanism by which the Mashan Group arrived at its present position between the Siberian and North China Cratons is poorly constrained, but it appears likely that, along with the North China, South China and Tarim Blocks, it underwent a northward drift from an initial location off northern Australia to finally dock with the Siberian Craton in the Late Permian to Late Jurassic.  相似文献   

广州小北路黑人聚居区社会空间分析   总被引：37，自引：6，他引：31  

李志刚  薛德升  Michael Lyons  Alison Brown 《地理学报》2008,63(2):207-218

1978 年改革开放带来中国城市的快速转型。近年来, 针对经济转型背景下中国大城市 的社会空间研究很多, 但对在全球化影响下出现的跨国移民族裔聚居区的研究尚不多见。对 广州黑人聚居区展开研究, 以越秀区小北路为例, 探讨其社会空间特征与演进机制。研究采 用微观视角, 针对典型案例进行问卷调查和半结构式访谈。研究表明, 广州黑人聚居区与西 方同类族裔社会区存在诸多差异。小北路黑人聚居区因全球化下新的“自下而上”的跨国经 济联系而生, 因广州城市的商贸文化、宗教历史、贸易网络和地理气候条件而兴, 其跨国移 民多为来自西非地区的族裔散居者/ 漂泊者(Diaspora), 其人口构成异质多元, 且流动性强。 小北路的社会空间机制既包含被动隔离也包含主动聚居, 其经济形态已经开始向“族裔聚居 区经济”(ethnic enclave economy) 发展。  相似文献   

Advancing development projects through mega-events: the 2010 football World Cup and bus rapid transit in South Africa     

Astrid Wood 《Urban geography》2019,40(4):428-444

In 2010, the focus of the sporting world was on South Africa, the first African country to host a Football World Cup, and the largest mega-event ever held on the continent. Mega-events like the World Cup have become instruments for governments seeking material improvements to highways and telecommunications as well as the more elusive nation-building and sanguine legacies. Whereas the literature typically concentrates on stadia and sports-related infrastructure, this paper focuses on bus rapid transit (BRT) as an “indirect legacy” to understand the way in which cities exploit the financial and political capital made available to advance projects long delayed behind more pressing endeavors. The compressed time horizons, unlocked financing and focused planning can be a “mixed blessing” however by limiting the scope of the project to the event. The paper concludes that in South Africa advancing development through the World Cup reinforced state authority and legitimacy.  相似文献   

基于报业话语的广州非裔社区的空间想象分析   总被引：4，自引：0，他引：4  

安宁  冯秋怡  朱竑 《地理学报》2019,74(8):1650-1662

使用文本分析和访谈的方法,本文检视了2007-2017年广州报业对广州非裔群体及非裔社区的话语表征。研究发现,受媒体自身对新闻素材的要求以及地方政治实践对媒体的影响,早期的广州报纸构建了指向性明确、有符号意味且被污名化的非裔空间地图。早先的话语产生了消极的社会影响,且一定程度上激化了非裔群体和地方社会的矛盾。其后,随着宏观政治格局的变化,尤其是置于构建社会主义和谐社会与中非合作论坛等语境时,广州报业媒体对于非裔报道致力于塑造中非发展共同体的地理想象,构建积极的广州非裔和非裔社区的形象,以期重构非裔社区的意义。广州报业的非裔话语是族裔社区空间形象构建过程,进而成为地方政治、国家政治和国际政治持续投影、纠葛和变化的地理再现。研究从社会文化地理学和政治地理学的角度丰富了对族裔社区划界、空间生产和地理想象的理解,试图建立报业舆论与地缘政治的地理视角联结。从实践和应用的角度来讲,本文探讨了全球化背景下媒体话语对跨境文化交融带来的挑战和影响,对于实现全球化背景下的中外多元文化交融与协商、实现良性的国际关系互动具有一定的参考价值。  相似文献   

非洲加蓬×区块油气成藏条件及勘探潜力分析   总被引：1，自引：0，他引：1  

张波 《海相油气地质》2006,11(1):30-34

加蓬×区块钻遇的最老地层是上白垩统,自下而上分为Azile组、Anguille组、Pointe-Clairette组及Point-Gentile组。上覆新生界主要分布于工区的西南部,地层比较齐全,工区东北部大部遭受剥蚀。Anguille组为半深海相泥岩夹粉细砂岩,分布全区,是主要的产油层之一。Pointe-Clairette组按岩性划分为上下两段(上PC段和下PC段),它们也是重要的产油气层。工区存在上白垩统Azile组和下白垩统Madiela组,N′Toum组三套烃源岩。区域盖层主要包括Anguille组和下PC段的海相泥岩;下白垩统盐岩也是一套十分优质的区域盖层。工区有四套储盖组合,主要为自储自盖和下储上盖。油气藏类型有(断裂)背斜油气藏、断裂鼻状构造油气藏、断块油气藏等。已有8口井在上、下PC段和Anguille组获得工业油气流,控制含油面积5.4km2,石油地质储量352.1×104t,预测含油面积26.4km2,石油地质储量4102.8×104t。在上、下PC段和Anguille组等三个地层中共识别出构造圈闭62个,圈闭总资源量约5×108t。  相似文献